This deregistration occurred only in the last few days. I was able to use the Store app no problem last week. It clearly has something to do with the website outage that occurred late last week and on the weekend.

If enTourage folds, you won't be able to register it, but it won't matter because registration only affects operations against the enTourage servers.

You will still be able to do the Adobe registration separately, though, by connecting the USB to a PC and using Adobe Digital Editions.